The present invention relates to a method and a device for driving at least one electromagnetic load, in particular a solenoid valve, for controlling the injection of fuel into an internal combustion engine, using a drive circuit equipped with electronic switching means and at least one booster capacitor. The booster capacitor has a first step in which voltage of the booster capacitor is recharged to a desired value influencing the opening speed of the injection valve, and thus the injection time, each time the booster capacitor is partially or completely discharged.
A method of this type and a device of this type are described in German Patent No. 195 39 071.
In common rail fuel injection systems, fuel mass metering for a cylinder is generally controlled by an injection valve. Metering precision is determined, among other things, by how fast the injection valve opens. The opening speed of the injection valve is accelerated by applying a high voltage, supplied from a booster capacitor, to the injection valve. The booster capacitor voltage must be returned to the desired value after the booster capacitor is completely or partially discharged during injection. This recharging operation is carried out using an electric circuit and takes a certain amount of time. If multiple injections take place in such rapid succession that an insufficient amount of time remains to completely recharge the booster capacitor, an undefined voltage is set at the booster capacitor. The failure of the booster capacitor voltage to return to the desired value at the beginning of injection causes the injection valve to open at different times, thus also producing different fuel masses. The different fuel masses increase exhaust emissions and decreases engine efficiency.
According to the object of German Patent No. 195 39 071 mentioned above, the booster capacitor is charged by selectively activating multiple switching means in a way that accelerates power-on and minimizes overall power consumption. Provided for this purpose are control means which drive the switching means in such a way that at least the power released during the transition from an inrush current value to a holding current value can be stored in the booster capacitor.
In light of the above remarks, an object of the present invention is to drive an electromagnetic load with sufficiently precise timing to improve, in particular, the fuel metering accuracy in an internal combustion engine having a common rail fuel injection system.
DC/DC converters are also frequently used to charge the booster capacitor.
According to one embodiment, the present invention also minimizes power loss when driving the electromagnetic load.
In a method according to the present invention, the above-mentioned object is achieved by detecting at least one operating state of the internal combustion engine and regulating the intensity of the required recharging current and/or the required recharging time necessary for the booster capacitor, at least as a function of the operating state.
According to an advantageous embodiment of the above method, the intensity of the recharging current and, correspondingly, the recharging time are defined and adjusted to the recharging current during regulation. This step makes it possible to advantageously minimize the power loss.
In situations where multiple injections must take place in rapid succession, for example when switching from stratified charge mode to homogeneous mode during direct gasoline injection or in the case of pre-injection or post-injection (e.g. to regulate the catalytic converter), the normal recharging time is insufficient. If this is required, the method according to the present invention regulates the recharging current intensity and/or the recharging time as a function of these additional engine control requirements.
A further step is to measure the voltage of the booster capacitor and regulate the recharging current and/or recharging time as a function of the measured voltage at the booster capacitor.
Another embodiment allows the calculated injection time to be corrected using a correction value representing the difference between the measured voltage and the desired voltage at the booster capacitor by correcting the calculated injection time with the correction value in a further step, thus forming a corrected injection time.
A device achieving the above object for driving at least one electromagnetic load, in particular a solenoid valve, for controlling the injection of fuel into an internal combustion engine, using a drive circuit equipped with electronic switching means and at least one booster capacitor and having recharging means which recharge the booster capacitor voltage to a desired value is characterized in that the recharging means are functionally connected to means for detecting at least one operating state of the internal combustion engine and have regulating means for regulating the intensity of the recharging current needed for the desired voltage value and/or the necessary recharging time, at least as a function of the operating state of the internal combustion engine detected by the detecting means.